Journal of Geosciences, 54 (2009), 73–82

DOI: 10.3190/jgeosci.040

Original paper

Tsumoite and associated tellurides from the Au deposit
Libčice near Nový Knín, Czech Republic: mineralogy andgenetic significanceJiří Sejkora1*, Jiří Litochleb1, Jakub Plášil1, Bohuslav Bureš2
Department of Mineralogy and Petrology, National Museum, Václavské nám. 68, 115 79 Prague 1, Czech Republic; jiri_sejkora@nm.cz
Plevenská 3111, 143 00, Prague 4, Czech Republic*
Corresponding author
1
2

A mineral association with dominant pyrrhotite, tsumoite and gold, accompanied by minor tetradymite and pilsenite, hasbeen found in material from the main vein of the abandoned Au deposit Libčice near Nový Knín, 25 km SSW of Prague,
central Bohemia, Czech Republic. Tsumoite forms abundant silvery grey tabular aggregates up to 1–4 mm in size. The
mineral is grey–white to very weakly beige-coloured in reflected light, anisotropic, with VHN microhardness 68 (63–76)
kg/mm2, with KVH = 1.21. Chemical analyses (electron microprobe) of matrix tsumoite yield Pb = 0.27, Cd = 0.12,
Bi = 61.12, Te = 37.97, S = 0.01 and total of 99.50 wt. %, which corresponds to an empirical formula of Bi0.99Te1.00 basedon 2 apfu. The chemical composition of Bi-rich schlieren-like domains within the tsumoite is Pb 0.20, Cd 0.09, Bi 63.06,
Te 36.44, S 0.01, total 99.80 wt. %, and corresponds to empirical formula Bi1.02Te0.97 on the basis of 2 apfu. Both compositional varieties of tsumoite exhibit relatively small non-stoichiometry in Bi:Te ratio with respect to the ideal formula.
The observed compositional range of tsumoite from Libčice corresponds to data published for this mineral species.
Tsumoite is trigonal with space group P-3m1 and unit-cell parameters a 4.4204(9)–4.4210(8), c 24.043(7)–24.055(6) Å,V 406.9(1)–407.2(1) Å3. Pilsenite forms rare cleavable aggregates up to 80 μm. Its chemical composition Pb 0.09,
Cd 0.12, Bi 67.63, Te 31.46, total 99.30 wt. % yields the empirical formula (Bi3.96Cd0.01Pb0.01)Σ3.98Te3.02 (based on 7 apfu).
Younger tetradymite occurs in tiny irregular aggregates which partly overgrew and replaced tsumoite in association
with native gold along fractures. The chemical composition of the tetradymite – Pb = 0.04, Cd = 0.11 Bi = 59.07,
Te = 36.08, S = 4.50, total = 99.78 wt. % – corresponds to an empirical formula (Bi2.00Cd0.01)Σ2.01Te2.00S0.99 (based on
5 apfu). Associated pyrrhotite yielded formula Fe1-xS with x values in the range 0.13–0.14. Gold contains low Ag (up to
4 wt. %) and Hg (up to 1 wt. %). The studied mineral association formed at elevated temperatures (>300 ºC), probably
at two stages differing in bismuth activity, as well as fS2 and fTe2 values. Alternatively, the two stages could have reflectedvariation of hydrothermal and metamorphic process in space and time.
Keywords: Bismuth-tellurides, tsumoite, X-ray powder diffraction data, chemical composition, Libčice gold deposit, Czech Republic
Received: 19 January 2009; accepted 8 April 2009; handling editor: R. Skála

1. Introduction
Bismuth-tellurides and Bi-sulphotellurides are characteristic accessory minerals of gold, gold-copper andbase metal ore deposits of magmatic, hydrothermal andmetamorphogenic type. The investigations of formation
conditions and crystal chemistry (in particular the scopeof possible non-stoichiometry and disorder character ofcrystal structure) brings information on ore genesis. For
this reason, these minerals have been intensively studied
recently (Gu et al. 2001; Ciobanu et al. 2006, 2009a;
Cook and Ciobanu 2004; Cook et al. 2007a, 2007b;
Parafiniuk et al. 2008; Tooth et al. 2008 and others).
Tsumoite, BiTe, first described in 1978 on material
from the type-locality Tsumo Cu-Zn-Pb skarn deposit,
Japan (Shimazaki and Ozawa 1978), belongs to the tetradymite group of Bi-tellurides. The main problem in nomenclature of minerals in the Bi–Te system relates to papers of Bayliss (1991), which presumed that there exists a

single solid-solution phase (Bi-rich tsumoite) with Bi and
Te in proportions of 1.35 to 2.61. This presumption of thecharacter of Bi-for-Te substitution has not been confirmedby new data. In difference to some other discontinuous
solid solution series in the Bi–Te–Se–S system (Ciobanu
et al. 2009b), tsumoite exhibits perfect stoichiometry inmajority of occurrences or shows limited compositionalvariation with c. 42–50 at. % Te, corresponding to solidsolution of tsumoite phase in the binary system Bi–Te(Okamoto and Tanner 1990). According to Cook et al.
(2007b), even in this narrow range there are several
discrete phases (known from synthesis experiments),
such as Bi8Te7, Bi22Te21, Bi32Te33, Bi14Te15, Bi26Te29 and
Bi8Te9 with 46.7, 48.8, 50.8, 51.7, 52.7 and 52.9 at. %Te. Broader solid-solution for tsumoite (exceeding therange of 42–50 at. % Te) has been described by Dobbe(1991) for Bi–Te compounds from Tunnaberg, Sweden,
and by Cabri and Laflamme (1976) for “wehrlite” from
Cu-Ni deposits of the Sudbury area, Canada. However, it
www.jgeosci.org

Jiří Sejkora, Jiří Litochleb, Jakub Plášil, Bohuslav Burešis probable that some of the chemical analyses publishedin these papers correspond to other minerals in the tetradymite group (e.g. hedleyite, pilsenite, unnamed Bi2Teetc.) (Cook et al. 2007b) or they may result from disorderon the lattice scale with nanoscale domains of structureswith different composition (Ciobanu et al. 2009b).
Tsumoite occurrences in the Czech Republic have been
described on the basis of energy dispersive microanalysis of microscopic aggregates (inclusions up to several
μm across and microscopic intergrowth aggregates withother opaque minerals) in material from the gold deposits
at Kašperské Hory (Scharmová and Pertoldová 1990)
and Vacíkov–Petráčkova hora (Pertoldová and Šulcová
1994) as well as from the Zadní Chodov uranium deposit(Scharmová 1998). Tsumoite has also been described asinclusions up to 30 μm in size, in association with Pd minerals and native bismuth in Cu-Ni sulphide mineralization
at Staré Ransko deposit (Vavřín et al. 1997; Vavřín andFrýda 1998; Pašava et al. 2003). The first occurrence in
the Czech Republic of a macroscopic intergrowth of tsumoite with tetradymite and tellurobismutite was describedby Litochleb et al. (2005) from gold-bearing quartz veinsat Bytíz–Staré hory, near Příbram.

2. Geological setting
The Libčice deposit is situated on the eastern slopes ofthe Hořice hill west of Libčice, c. 4 km south of the townof Nový Knín in central Bohemia, Czech Republic. It
represents a locality with the largest gold accumulation in
the Nový Knín gold-bearing area with estimated historical production of two tons Au. Mining took place mainly
during the Middle Ages, with the last activity during thefirst half of the 20th century. Workings reached a depth ofnearly 200 m in the Middle Ages and belong thus, besides
the Jílové gold-bearing district, to the deepest ones in
Bohemia (Litochleb 1976, 2003). Exploration of deeper
levels (from 300 to 400 m) started in 1945 and was terminated in 1957 (Malachov 1953; Havlíček 1959).
The deposit is located in the Dražetice volcanic body(dacite) of the Kozí Hory Belt and in tuffitic schists of
Neoproterozoic age. At the eastern flank, and toward
deeper levels, the intrusive body of the Variscan Libčice
biotite granite of Central Bohemian Pluton limits the deposit and was responsible for its thermal metamorphism.
Mineralization of the vein type is tied to steep lamprophyre dykes with two different trends. The main Libčice
vein (known under historical name Mladá Kamlová
Zone; Amort 1942) follows an east–west trending spessartite dyke. A second vein trend (Stará Kamlová Zone)
accompanies north–south trending kersantite dykes.
Both spessartite and kersantite dykes are older than ore
mineralization and obviously than the Libčice biotite
74

granite (Morávek et al. 1992). These gold deposits are
now considered examples of the so-called RIRG (reduced
intrusion-related gold) type of gold deposits (Zachariáš
et al. 2001). In contrast with other Au deposits of theBohemian Massif, Au ore mineralization and surrounding rocks of the Libčice deposit were clearly thermally
metamorphosed by the younger Libčice biotite granite.
The Libčice main vein with a steep dip of 75–90° to
the north was opened at the level of seven galleries to adepth of nearly 400 m below surface. The main parts ofthe vein have been exploited to a depth of 200 m. The
mineralized parts of the vein form a steep ore column
250–350 m long, bound at depth by the contact to the
granite intrusion. In the east and west, the ore column islimited by wedging-out of the quartz vein and the hostlamprophyre dyke. Shallow dip of the granite contact
toward the west results in a wide zone of contact metamorphism of Neoproterozoic rocks and gold-bearingveins. The older age of the lamprophyre and gold-bearing
vein is documented by the presence of their xenoliths in
granite in a distance up to several metres from the contact(Pivec and Šrein 1987). The vein of massive grey–whitequartz is on average 0.2–0.3 m wide, locally it exceeds
1 m. The content of ore minerals is variable, usually low.
Gold of a high fineness is typically finely disseminatedbut it forms some local macroscopic aggregates. Gold
content is highly variable, values of 10–270 g Au/t, locally up to as much as 1,000 g Au/t, were reported in old
workings. There is a weak decline in the gold content
with depth, but the width of veins is strongly reduced.
The gold-bearing quartz vein is cut by flat lying dykes of
aplite and pegmatite and disrupted by fractures trending
N–S and E–W, often filled by calcite (with palygorskite)or rare galena with sphalerite (Morávek 1958).
The granular texture of vein quartz and the presenceof contact metamorphic silicates (such as wollastonite,
diopside and grossular–andradite) in mineralized quartz
gangue indicate thermal recrystallization. The situation points to overprinting of hydrothermal products bymagma-related thermal recrystallization and to specificminerogenetic conditions corresponding to epidote-amphibole or amphibole hornfels metamorphic facies.
Ore mineralization is characterized by abundant hexa­
gonal pyrrhotite, less common pyrite, arsenopyrite andmolybdenite, gold in two generations (gold I with 2–5
wt. % Ag and younger gold II with 12–13 wt. % Ag),and fine-grained aggregates of Bi-tellurides (Malec etal. 1985; Litochleb and Šrein 1994; Šrein et al. 1995).
Zachariáš et al. (1997) proposed the following crystallization succession: quartz I, pyrrhotite → arsenopyrite
I, pyrite I → loellingite → gold, Bi-tellurides, calcite
I → quartz II, (Co-) arsenopyrite II, pyrite II, gold II,
CoSbS → pyrrhotite, chalcopyrite, tetrahedrite → pyrite
III, calcite II, quartz III.

Bi-telluride association from the Libčice deposit

Previous studies at this deposit resulted in the description of several minerals belonging to the Bi-tellurides
group. Slavík (1918) reported occurrences of so-called
tellurobismuthite (rich finds at the third level). Besides
that were identified tetradymite, joséite B (Šrein et al.
1995) and silvery white tabular crystals, ascribed, without
compositional data, to ‘wehrlite’ (Sobotka 1959), later
re-defined as pilsenite (Ozawa and Shimazaki 1982). The
occurrence of Au and Ag tellurides, reported by Hofmann(1912), has not been confirmed by subsequent studies.
According to Malec et al. (1985), these minerals most
likely represent microscopic intergrowths of gold with
Bi-tellurides.

3. Analytical techniques
Polished sections of the studied samples from Libčice
were prepared for optical investigation, measurementof microhardness and chemical analysis using standard
diamond polishing techniques. Optical properties in reflected light were observed with a Nikon Eclipse ME600
microscope. The Vickers microhardness of tsumoite wasmeasured using a PMT-3 instrument with 15g load (calibrated on halite crystal with 5g load, indentor exposure
15 s, average value was calculated from 20 measurementson three grains).
Back-scattered electron (BSE) images were acquired
and quantitative chemical compositions of minerals determined with a Cameca SX100 electron microanalyzer(Faculty of Science, Brno) operated at the following
conditions: wave-length dispersive analysis, 25 kV, 20
nA, electron beam diameter less than 1 μm. The following standards were used: Ag (AgLα), Au (AuLα), Bi(BiMβ), Bi2Te3 (TeLβ), CdTe (CdLβ), chalcopyrite (SKα),
Cu (CuK α), FeS 2 (FeK α), pararammelsbergite (AsL β),
PbCl2 (ClKα), PbSe (PbMα, SeLβ) and Sb (SbLβ). The
abundances of the above elements, if not included inanalytical data tables, were measured, but the values were
below the respective detection limit (0.01–0.03 wt. % forindividual elements). Measured data were corrected using
the PAP software (Pouchou and Pichoir 1985).
A handpicked sample of tsumoite was used for powder
X-ray diffraction experiments. The continuous mode of
the PANalytical X’Pert Pro powder diffractometer (Faculty of Science, Charles University, Prague) operating at
40 kV and 40 mA with X’Celerator detector was used.
Firstly, the sample was measured at Bragg-Brentano geo­
metry. The sample studied was placed onto the surface
of a flat silicon monocrystal wafer from the suspensionof acetone in order to minimize complicated background.
The X-ray powder diffraction data were collected from 3°
to 75° 2θ with integrated step of 0.02° 2θ and virtual time
per integrated step of 350 seconds. Later, small amountof sample powder was mounted on a thin glass fibre
onto goniometric head and scanned in Debye-Scherrer’s
geometry. For unit-cell parameters the powder X-ray diffraction pattern was collected in the range of 6–75° 2θ
with CuKα radiation (Ni-filter, integrated step 0.02° 2θ,virtual time 2500 s, sample was rotated). In both cases,
the position of each diffraction maxima was refined using profile shape function Pearson VII by software ZDS(Ondruš 1993) and was used for unit-cell parameterrefinement by software of Burnham (1962) based onleast-squares method.

4. Results and discussion

4.1. Sample description
The several studied samples were collected in 1955 on
the 5th level of the Libčice mine in the main vein of
the deposit, west of the shaft, near the contact with the
Libčice granite. The samples represent a fine-grained
black–green, hornfels-like rock with nearly massive greyquartz, and showing slickenside surfaces. The rock contains irregular granular sulphide aggregates (pyrrhotite,
pyrite, arsenopyrite) 0.X to 5–10 mm in size, fine-grained
deep yellow gold and abundant silvery to light yellowish
flaky tsumoite aggregates 1–4 mm across. Bi-tellurides,
gold and sulphides form mutual intergrowths.

4.2.	Tsumoite
Tsumoite is by far the most abundant Bi telluride in thestudied mineral association. Some parts of the samples
contain tsumoite in amounts comparable to the mostabundant sulphide – pyrrhotite. Tsumoite forms irregular
platy aggregates 1–4 mm long, showing a weak cleavage.
On fresh fracture the mineral has an imperfect and silvery
white metallic lustre. Compared to other Bi tellurides(tetradymite, tellurobismuthite etc.) it is clearly darker. In
reflected light tsumoite is grey–white with a weak creamy
shade, under crossed polarizers it is weakly anisotropic
and shows grey–brown colour effects.
Vickers microhardness VHN15g = 68 (63–76) kg/mm2
with anisotropy coefficient KVH = 1.21 was measured
on the studied tsumoite. There are few such publisheddata on tsumoite microhardness, because of the generally very fine grain size of the mineral. Shimazaki andOzawa (1978) reported values 51–90 kg/mm2, Pavlova
et al. (1988) measured on tsumoite from BiTe–Bi3S5 decomposition structures VHN20g = 101 (93–108) kg/mm2.
This value is influenced by higher hardness of the intimately intergrown phase Bi3S5. Litochleb et al. (2005)
reported VHN15g = 109 (93–133) kg/mm2 with anisotropy75Jiří Sejkora, Jiří Litochleb, Jakub Plášil, Bohuslav Bureš

coefficient KVH = 1.43. The differences in measured microhardness of tsumoite from the localities Bytíz–Staréhory (Litochleb et al. 2005) and Libčice (this study) relate to hardness anisotropy of the second order (reticularanisotropy) in sections with different crystallographic
orientations. In sample from Libčice were measured sections approximately normal to the basal plane, showing
lower microhardness, whereas that from Bytíz–Staré hory
was cut nearly parallel to the basal plane. The measured
values indicate that tsumoite shows usually a higher
microhardness in comparison with other phases in the
Bi–Te–S system.
A detailed examination of the BSE images resulted in
the recognition of irregular schlieren-like domains in partsof tsumoite aggregates (Fig. 1). A lighter Bi-rich phaseof the schlieren passes gradually, without clear boundary,
into darker Bi-poor matrix. Quantitative chemical analyses(Tab. 1) show that the tsumoite matrix (Figs 2–3) has theaverage Bi:Te ratios 0.99 (0.94–1.04) and Te contents of
50.3 (48.5–51.5) at. %. The empirical formula for matrix
tsumoite (average of 27 spot analyses) is Bi0.99Te1.00, basedon 2 apfu, i.e. perfect stoichiometry within the range ofanalytical error. The lighter schlieren with Bi:Te ratio
1.06 (1.03–1.10) and 48.5 (47.5–49.2) at. % Te represent Bi-rich variant of tsumoite with empirical formula
Bi+

0 70

5

65

published data for tsumoite
tsumoite (matrix), Libèice (this paper)
tsumoite (schlieren), Libèice (this paper)
pilsenite, Libèice (this10
paper)
ideal compositions

60

Bi4Te 3

15

55

20

50 BiTe

25

S+Se

30

45

Bi3Te 4

35

40

45

50

Te

55

Fig. 2 Part of Bi+ vs Te vs S + Se ternary plot for Bi tellurides from
Libčice. Bi+ = Bi + Sb +Pb + Cd + Ag + Fe + Cu + Hg; published data
for tsumoite are taken from papers of Shimazaki and Ozawa (1978),Zavjalov et al. (1978), Gamjanin et al. (1980), Gu et al. (2001), Cook
and Ciobanu (2004), Ferenc (2004) and Litochleb et al. (2005).

Fig. 1 A BSE image of irregular schlieren of lighter Bi-rich tsumoite
passing gradually, without a clear boundary, into a matrix of darker
tsumoite.

Tab. 1 Representative chemical composition of two types of tsumoite from Libčice near Nový Knín (wt. %). Number of atoms based on 2 apfu
tsumoite – matrix

tsumoite – schlieren
range

1

2

0.15

mean*
(n = 14)*0.20

0.14–0.32

0.01

0.36

0.09

0.02–0.18

0.18

61.80

62.63

63.06

62.47–64.33

62.52 62.47 63.14 63.15 64.22

37.79

36.88

36.44

35.40–37.22

37.22 36.83 36.24 36.48 35.66
0.00

range

1

2

3

4

5

Pb

mean*
(n = 27)*
0.27

0.09–0.52

0.43

0.27

0.18

0.23

Cd

0.12

0.03–0.36

0.03

0.15

0.15

0.07

Bi

61.12

59.88–62.63

59.90

60.84

61.23

Te

37.97

36.88–39.10

39.09

38.83

37.50

3

4

5

0.24

0.32

0.27

0.16

0.11

0.12

0.05

0.02

S

0.01

0.00–0.05

0.00

0.05

0.00

0.00

0.00

0.01

0.00–0.11

Total

99.50

98.50–100.77

99.45 100.13

99.05

99.89 100.02

99.80

99.66–100.60 99.93 99.66 99.92 99.94 100.07

Pb

0.004

0.007

0.004

0.003

0.004

0.002

0.003

0.000 0.004 0.005 0.004 0.003

Cd

0.004

0.001

0.004

0.004

0.002

0.011

0.003

0.005 0.003 0.004 0.001 0.001

Bi

0.987

0.963

0.971

0.995

0.996

1.011

1.024

1.010 1.014 1.020 1.025 1.046

Te

1.004

1.029

1.015

0.998

0.998

0.975

0.969

0.985 0.979 0.959 0.970 0.951

S

0.001

0.000

0.005

0.000

0.000

0.000

0.001

0.000 0.000 0.012 0.000 0.000

Sum

2.000

2.000

2.000

2.000

2.000

2.000

2.000

Bi:Te

0.99

0.94

0.96

1.01

1.01

1.04

1.06

*

0.94–1.04

mean and range of all measurements, followed by selected representative analyses

76

0.00

0.11

0.00

0.00

2.000 2.000 2.000 2.000 2.000
1.03–1.10

1.03

1.04

1.06

1.06

1.10

Bi-telluride association from the Libčice deposit

Tab. 2 X-ray powder diffraction pattern of tsumoite from Libčice (Å)

30

at. % S+Se

20
15

calculated data

tsumoite (matrix), Libèice
tsumoite (schlieren), Libèice
tetradymite, Libèice
pilsenite, Libèice

25

MeX

10

Me4X3

5

Me2X3

0

35

40

45

50

55

60

65

at. % Te

Fig. 3 Plot Te vs. S + Se (at. %) for studied Bi tellurides and sulphotellurides.

Bi1.02Te0.97 (average of 14 spot analyses, based on 2 apfu).
Yet, their composition falls within the range 42–50 at. %Te published for tsumoite solid solution in the binary
system Bi–Te (Okamoto and Tanner 1990). The observed
non-stoichiometry for tsumoite from Libčice probably
indicates variation of conditions in the course of crystallization (such as changes in the Bi:Te ratio, temperature
and/or pressure – Melnikov et al. 2005).
A X-ray powder diffraction pattern for tsumoite from
Libčice was measured, beside the usual Bragg-Brentano
setup, also using the Debye-Scherrer’s geometry to reduce preferred orientation of the sample, caused by theperfect cleavage of the mineral. Decreasing relative intensity of the 00l diffraction type maxima (Tab. 2) indicatesthat the use of Debye-Scherrer’s geometry resulted inminimizing the preferred orientation effect. The obtained
patterns correspond to theoretical values calculated fromthe BiTe crystal structure (Yamana et al. 1979) and datareported for natural tsumoite by Shimazaki and Ozawa(1978), Zavjalov et al. (1978) and Gamjanin et al. (1980).
Refined unit-cell parameters for tsumoite from Libčice

h

k

l

dcalc.

Icalc.

00

1

24.002400

212.001

1

0

0

3

8.001

1

0

0

5

4.800

Bragg-Brentano Debye-Scherrer
dobs.

Iobs.

dobs.

Iobs.

4

4.798

28

4.806

15

3.776

2

3.785

14

3.229

100

0

1

1

3.783

4

0

1

3

3.455

1

1

0

4

3.229

100

3.229

100

1

0

6

2.767

1

2.775

2

0

1

8

2.362

40

2.364

35

2.365

35

1

1

0

2.212

36

2.211

7

2.212

21

2.189

4

2.189

12

1

0

9

2.189

3

0

1

10

2.034

1

1

1

5

2.009

1

2.010

11

2.007

9

1

1

-5

2.009

1

2.010

11

2.007

9

0

0

12

2.000

7

2.004

25

2.007

9
13

2

0

1

1.909

1

1.908

2

0

2

4

1.825

20

1.825

5

1.825

0

1

13

1.663

2

1.665

4

1.666

8

2

0

8

1.614

13

1.615

10

1.615

17

0

2

9

1.556

1

1.556

2

1.557

11

1

1

12

1.483491.485410

1.4851

20

1

1 -12

1.483491.485410

1.4851

20

0

0

17

1.41191

1.41421

1.4126

3

1

2

-4

1.40749

1.40722

1.4064

17

2

1

4

1.40749

1.40722

1.4064

17

1

0

16

1.396861.400111

1.3984

5

2

0

13

1.32921

1.33042

1.3293

1

2

1

-8

1.303961.30432

1.3042

13

1

2

8

1.303961.30432

1.3042

13

3

0

0

1.27686

1.27472

1.2749

9Theoretical data (with I calc. > 0.6) were calculated by program Lazy
Pulverix (Yvon et al. 1977) using the crystal structure information on
synthetic tsumoite (Yamana et al. 1979)

Tab. 3 Unit-cell parameters of tsumoite indexed to the trigonal space group P-3m1

Libčice BB*
Libčice D
synthetic
TsumoPříbram-Bytíz
Burčaginkan
Tyrnyauz
Ilkovcy-Podulky
Tyrnyauz
Miller-Kopper
Alekseevskoje*

this paper
this paper
Yamana et al. (1979)
Shimazaki and Ozawa (1978)
Litochleb et al. (2005)
Zavjalov et al. (1978)
Zavjalov et al. (1978)
Zavjalov et al. (1978)
Zavjalov et al. (1978)
Zavjalov et al. (1978)
Zavjalov et al. (1978)a [Å]
4.4210(8)4.4204(9)4.423(2)4.422(2)4.423(1)
4.427
4.425
4.421
4.411
4.408
4.408

c [Å]
24.055(6)24.043(7)24.002(6)24.05(2)24.01(1)
24.06
24.04
24.06
24.18
24.18
24.18

V [Å3]
407.2(1)406.9(1)
406.6
407.3
406.8(2)
408.4
407.6
407.2
407.4
406.9
406.9

BB – Bragg-Brentano, D – Debye-Scherrer geometries77Jiří Sejkora, Jiří Litochleb, Jakub Plášil, Bohuslav Bureš(Tab. 3) compare closely with data published for thismineral. Differences in parameters obtained using the two
measurement geometries are in the range of calculated
standard deviations.

4.3.	Tetradymite
In the studied mineral association tetradymite is younger
than tsumoite and comparatively rare. Typically it
forms irregular minute aggregates (1–10 μm), which
partly overgrow and replace older tsumoite associatedwith gold (Fig. 4). Examples of irregular aggregates of
tsumoite up to 100 μm, almost completely replaced bytetradymite and gold, are scarce (Fig. 5). Tetradymite inintergrowth with Bi–Te phases is distinctly darker grey;
it is anisotropic and shows bireflection with grey togrey–brown colour effects. Chemical composition of theFig. 5 Irregular tsumoite aggregates (light grey) extensively replaced byyounger tetradymite (dark grey) and gold (white) (BSE image).

studied tetradymite (Tab. 4) is near the ideal compositionof this mineral (Fig. 3). The Sb and Se are not present
in detectable abundances, the maximum content of Cd
is 0.01 apfu and Pb content lower than 0.01 apfu. The
average Te:S ratio 2.01 (1.90–2.24) is near the theoretical 2:1. The empirical formula of tetradymite (averageof 5 spot analyses) is (Bi 2.00Cd0.01)Σ2.01Te2.00S0.99, basedon 5 apfu.

4.4. Pilsenite

Fig. 4 Dark irregular aggregates of tetradymite, which penetrate along
fractures, partly overgrow and replace older tsumoite (light grey) associated with gold (white) (BSE image).

Pilsenite has been observed as a single cleavable aggregate 70 by 80 μm in size, intergrown with gold (Fig. 6)
in quartz gangue. It is light grey in reflected light, compared to tsumoite it shows slightly higher reflectivity andunder crossed polarizers it is weakly anisotropic (withgrey–brown colour effects). Chemical composition of

Tab. 4 Chemical composition of tetradymite and pilsenite from Libčice (wt. %). Number of atoms based on 5 apfu (tetradymite) and 7 apfu
(pilsenite)
tetradymite

pilsenitemean (n = 5)

1

2

3

4

5

mean (n = 5)

1

2

3

4

5

0.04

0.08

0.00

0.09

0.00

0.00

0.09

0.08

0.07

0.16

0.06

0.08

Cd

0.11

0.11

0.14

0.17

0.08

0.04

0.12

0.08

0.12

0.16

0.13

0.11

Bi

59.07

59.42

59.17

59.07

59.11

58.58

67.63

67.48

68.18

67.47

67.06

67.98

Te

36.08

36.09

36.82

35.47

35.59

36.41

31.46

31.47

31.36

31.55

31.63

31.31

S

4.50

4.51

4.14

4.69

4.55

4.60

0.00

0.00

0.00

0.00

0.00

0.00

Total

99.78

100.22100.25

99.48

99.33

99.63

99.30

99.11

99.73

99.33

98.87

99.48

Pb

0.001

0.003

0.000

0.003

0.000

0.000

0.005

0.005

0.004

0.009

0.003

0.005

Cd

0.007

0.007

0.009

0.011

0.005

0.003

0.013

0.008

0.013

0.017

0.014

0.012

Bi

2.000

2.004

2.017

1.994

2.008

1.975

3.963

3.961

3.983

3.949

3.940

3.981

Te

2.000

1.994

2.055

1.961

1.980

2.011

3.019

3.026

3.000

3.024

3.043

3.003

S

0.992

0.992

0.919

1.031

1.007

1.012

0.000

0.000

0.000

0.000

0.000

0.000

Sum

5.000

5.000

5.000

5.000

5.000

5.000

7.000

7.000

7.000

7.000

7.000

7.000

Pb

78

Bi-telluride association from the Libčice deposit

pilsenite (Tab. 4) matches well the theoretical formula
Bi4Te3 (Figs 2–3). Minor Cd corresponds to 0.01 apfu, Pb
is lower than 0.01 apfu; Sb, S and Se were not detected.
Its chemical composition (average of 5 spot analyses)
yields a theoretical formula (Bi3.96Cd0.01Pb0.01)Σ3.98Te3.02,
based on 7 apfu.

4.5. Other ore minerals
Gold forms tiny grains, dendritic aggregates up to 1 mmor occurs as thin coatings on wallrock fractures close to
the quartz vein. Microscopic study shows that gold (A)forms subhedral grains up to 100 μm, which are older
than the pilsenite (Fig. 6) or tsumoite (Fig. 7). In otherplaces occur small irregular aggregates of younger gold(B), 5–30 μm across, which, together with tetradymite, areassociated with earlier tsumoite (Figs 4–5). Gold is deep
yellow in reflected light, and optically homogeneous, except for local and small tetradymite inclusions. The older
generation of gold (A) with an average composition of Ag= 3.58 (3.25–3.93), Au = 94.69 (93.83–95.63), Hg = 0.72
(0.30–1.08), Cu = 0.14 (0.11–0.17), Bi = 0.05 (0.02–0.10)
wt. %, corresponds well to data published previously for
older gold generation I from Libčice (Šrein et al. 1995;
Zachariáš et al. 1997). Gold in intergrowth with pilsenite
contains lower Ag (up to 0.061 apfu) and Hg (up to 0.005
apfu) than gold in association with tsumoite (Ag up to
0.070, Hg up to 0.010 apfu).

Fig. 7 Crystal of gold (white) overgrown by tsumoite (light grey) andreplaced from the margins by tetradymite (dark grey) (BSE image).

arsenopyrite. Chemical composition is very simple as no
additional elements are present in addition to Fe and S(Fe = 59.65–59.75, S = 39.48–40.01, total 99.17–99.66
wt. %). Iron content in pyrrhotite (calculated to 1 apfu S)
is 0.856–0.867 apfu, which for the empirical formulaFe1-xS yields value x = 0.13–0.14. Such a composition
falls in the range for natural pyrrhotites, for whichx = 0–0.17 was reported (Anthony et al. 1990). No indications of transformation of pyrrhotite to marcasite
have been observed either in reflected light or in BSE
images. On the other hand, the alteration of pyrrhotite tomarcasite is a characteristic feature of the younger (postmetamorphic) stages of mineralization in the studied vein(Šrein et al. 1995).

5. Conditions of formation

Fig. 6 Gold aggregate (white) overgrown by, and intergrown with, anaggregate of cleavable pilsenite (light grey). Tetradymite forms minutedark inclusions in gold (BSE image).

Hexagonal pyrrhotite strongly predominates inthe studied mineral association. It forms fine-grained
impregnations or irregular aggregates up to 1 cm inrecrystallized quartz. Pyrrhotite has a metallic lustre
and light beige–brown colour. In reflected light pyrrhotite is pinkish-brown, anhedral to subhedral and it ismostly replaced, except for small relics, by pyrite and

The studied mineralization with macroscopic Bi–Te
minerals and gold of high fineness belongs to Au–quartz
mineralization, which is widespread throughout theCentral Bohemian Metallogenetic Zone (Morávek et al.
1992). Compared to similar deposits and occurrences inthis zone (e.g. Jílové near Prague, Nový Knín, Mokrsko–Čelina), the studied locality differs by the presence ofyounger contact metamorphic phenomena, which affected
the mineralogical composition, structure of the gangue
and character of the ore mineralization.
The observed crystallization sequence: gold A → tsumoite (+ pilsenite) → tetradymite → gold B and relative
abundance of individual minerals permit to define at least
two stages of crystallization in this mineral association.
The more important first stage, which was responsible fordeposition of pyrrhotite, gold A, tsumoite (both varieties)
and pilsenite (all phases with ratio Me/(Te + Se + S) ≥ 1)
was characterized by high activity of bismuth at low

79Jiří Sejkora, Jiří Litochleb, Jakub Plášil, Bohuslav Bureš

values of fS2 (S-free Bi tellurides, presence of pyrrhotite)and locally variable but relatively high values f Te2 in hydrothermal fluids (Afifi et al. 1988; Cook and Ciobanu
2004 among others). The non-stoichiometry of the latertsumoite generation, the presence of its two chemicallydistinct varieties and the absence of native bismuth in theassemblage may indicate formation at elevated temperatures (>300 ºC) and somewhat variable conditions (e.g.,changing Bi:Te ratio, temperature and/or pressure). Basedon study of fluid inclusions from Libčice by Zachariáš
et al. (1997), the following formation conditions were
estimated for quartz and gold of the older generation:
T = 290 to 310 ºC and P = 1.2–1.6 kbar. Formation of
the abundant older pyrrhotite probably resulted frommetamorphic recrystallization of the original pyrite. The
second stage, products of which are subordinate, is characterized by a replacement of the older Bi–Te minerals
by tetradymite, gold B, and by an origin of pyrrhotite
of younger generation, pyrite and arsenopyrite. Thisdevelopment indicates a notable decline in Bi activity
and an increase in fS2 in hydrothermal fluids (Affifi et al.
1988). A straightforward interpretation of minerogenesis
at the Libčice deposit is significantly complicated byvariable manifestations of hydrothermal and, especially,
metamorphic processes in space and time. The two stages
probably can represent a “primary” hydrothermal episodeand a younger contact metamorphic (recrystallization)
overprinting event.

6. Conclusions
A mineral association consisting of dominant pyrrhotite, tsumoite and gold, with accessory tetradymite andpilsenite, has been identified in high-grade gold ore fromthe main vein of the Libčice deposit. Study of chemicalcomposition of tsumoite resulted in identification of its
stoichiometric (predominating matrix) and a Bi-rich (inthe form of schlieren) varieties. The compositional rangeof tsumoite from Libčice corresponds to data published
for this mineral. Coexisting tetradymite and pilsenite areclose to ideal stoichiometry, pyrrhotite is characterized by
the formula Fe1-xS with x values in the range 0.13–0.14;
gold contains low Ag (up to 4 wt. %) and Hg (up to
1 wt. %) admixtures.
The studied mineral association formed at elevatedtemperatures (>300 ºC), probably in two stages with declining activities of bismuth and variable fS2 and fTe2. The
origin of tetradymite after tsumoite and the replacementof older pyrrhotite by pyrite with arsenopyrite indicate asulphidation of the assemblage in the second stage. The
two stages probably represent a “primary” hydrothermal
episode and a younger contact metamorphic (recrystallization) overprinting event.
80

Acknowledgements The authors thank Radek Škoda
(Institute of Earth Sciences, Masaryk University, Brno)and Stanislav Vrána (Czech Geological Survey, Prague)
for their kind help with the analytical work and language
correction. The reviewers, Nigel John Cook and YvesMoëlo with handling editor Roman Skála are thanked fora number of constructive comments. The research was
financially supported by the grants 205/06/0702 (Grant
Agency of the Czech Republic) and MK00002327201(Ministry of Culture of the Czech Republic).

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